1. Field of the Invention
This invention relates to a platinum complex catalyst in the form of a modified platinum-vinyl siloxane complex having improved storage stability and useful as a hydrosilylation catalyst.
2. Prior Art
Hydrosilylation reaction represented by the following scheme is well known in the art and finds application in a variety of areas using curable silicone compositions. ##STR1##
This hydrosilylation reaction is to react SiH group-bearing compounds such as organohydrogensiloxane with CH.sub.2 .dbd.CH group-bearing compounds such as vinyl-bearing organopolysiloxanes in the presence of platinum catalyst. Of the platinum catalysts, initial ones are halogenated platinum compounds and microparticulate metallic platinum, for example, chloroplatinic acid disclosed in Speir, U.S. Pat. No. 2,823,218 and platinum-carrying char coal disclosed in Bailey, U.S. Pat. No. 2,970,150. From the standpoint of economical efficacy, efforts were made to improve the activity of catalysts. Since then, platinum-vinyl siloxane complexes have been frequently used. However, it is pointed out in JP-B 423/1980 that halide ions in platinum-vinyl siloxane complexes adversely affect the catalytic activity thereof. JP-B 28795/1971 and 23679/1972 disclose that platinum-vinyl siloxane complexes can be decomposed upon contact with water. It was thus recommended that platinum-vinyl siloxane complexes are stored at temperatures between 50.degree. C. and 50.degree. C.
However, we often encountered the phenomenon that platinum-vinyl siloxane complexes blackened and settled in summer. This phenomenon causes a trouble during storage and on subsequent use.
Efforts have also been made to improve the activity of platinum-vinyl siloxane complexes by minimizing the content of residual halide. For example, JP-A 136655/1981 discloses a platinum complex substantially free of inorganic halides. In contrast, JP-A 36573/1991 discloses a method for preparing a platinum-vinyl siloxane complex having high activity and storage stability even when more than 1 gram-atom of inorganic halide is present per gram-atom of platinum. We confirmed that the hydrolysilation catalyst obtained by this method lacked storage stability at elevated temperatures, blackened its outer appearance, gradually formed precipitates, and invited a decline of its catalytic activity.
Therefore, it is desired to overcome the above-mentioned problems during storage of platinum-vinyl siloxane complexes that they are sensitive to heat and moisture, lack storage stability, and tend to decrease their catalytic activity through coloring and formation of black precipitates, especially in summer. That is, it is desired to improve the storage stability of platinum-vinyl siloxane complexes without lowering their catalytic activity.